MINOR: tools: let dump_addr_and_bytes() support dumping before the offset

MINOR: tools: let dump_addr_and_bytes() support dumping before the offset

For code dumps, dumping from the return address is pointless, what is
interesting is to dump before the return address to read the machine
code that was executed before branching. Let's just make the function
support negative sizes to indicate that we're dumping this number of
bytes to the address instead of this number from the address. In this
case, in order to distinguish them, we're using a '<' instead of '[' to
start the series of bytes, indicating where the bytes expand and where
they stop. For example we can now see this:

       0x6bd634 <64 8b 38 e8 ac f7 ff ff]: debug_handler+0x84/0x95
 0x7fa4ea2593a0 <00 00 00 00 0f 1f 40 00]: libpthread:+0x123a0
       0x752132 <00 00 00 00 00 90 41 55]: htx_remove_blk+0x2/0x354
       0x5b1a2c <4c 89 ef e8 04 07 1a 00]: main+0x10471c
       0x5b5f05 <48 89 df e8 8b b8 ff ff]: main+0x108bf5
       0x60b6f4 <89 ee 4c 89 e7 41 ff d0]: tcpcheck_eval_send+0x3b4/0x14b2
       0x610ded <00 00 00 e8 53 a5 ff ff]: tcpcheck_main+0x7dd/0xd36
       0x6c5ab4 <48 89 df e8 5c ab f4 ff]: wake_srv_chk+0xc4/0x3d7
       0x6c5ddc <48 89 f7 e8 14 fc ff ff]: srv_chk_io_cb+0xc/0x13

(cherry picked from commit 003f5168e47f6755990b8315757ecd71ef684c56)
Signed-off-by: Aurelien DARRAGON <adarragon@haproxy.com>